A variety of image recording bodies are used as so-called ID cards including identification cards themselves, driving licenses and membership cards. In general, ID cards contain a portrait to identify the bearer of the card and various mentioned items. This portrait is usually made of a gradation image; therefore, it is called a gradation information containing image hereinafter simply referred to as a gradation image. The various mentioned items of an identification card include, for example, the bearer's place of residence, name, date of birth, position and the expiration date of the card's validity time, and those of a driving license are the bearer's name, date of birth, license number and type of license. These mentioned items are usually described by use of letters, figures or symbols; accordingly, these are called character information containing images hereinafter simply referred to as a character image.
Recently, there has come to be used ID cards carrying a gradation image formed by the sublimation thermal transfer method, because of the method's capability of forming fine images with ease. In general, the sublimation thermal transfer method means a method of forming a gradation image, such as a portrait, on an image receiving layer by the steps of contacting the image receiving layer of an image receiving sheet, which comprises a support and the image receiving layer provided thereon, with an ink layer of an ink sheet, which comprises a support and the ink layer containing a sublimation dye provided thereon, and transferring the sublimation dye onto the image receiving layer by imagewise heating.
However, this sublimation thermal transfer method is not necessarily satisfactory in dye fixation and liable to cause set-off or blur of image dyes.
In order to improve the fixation of dyes and protect the gradation image on ID cards, there has been practiced the transfer of a protective layer onto the surface of an ID card by means of hot stamping method.
But such a protective layer covers only image portions, which project from non-image portions and tend to retain residual resins called burrs on their periphery, thereby such a covering often impairs appearance of a card. Further, an unevenly applied heat in hot stamping is liable to cause thermal deformation or curling.